Fatigue Crack Paths 2003

The effective stress intensity factor range of the stress relieved specimen deviates

slightly from the expected values beyond a length of 14 mm. It is not clear whether this

is a closure effect or a shortcoming in the stress intensity calibration for this geometry.

In Fig. 4 are shown the data for the repair welded specimens tested over a range of

load ratios. Again, the ability of the T S Atechnique to measure effective stress intensity

factor ranges is clearly shown. A reduction in closure is apparent as the mean load is

increased. However, even at R=0.6 the experimental data deviate from the expected

values at crack lengths beyond 14 mm.

4550

Theoretical

R=0.1

1234505050

R=0.3

R=0.6

10

5

0

4

6

8

10

12

14

16

18

20

22

Crack length (mm)

Figure 4. Influence of meanload on modeI stress intensity factor ranges versus crack

length results for repair welded specimens using TSA.

The result of locating the crack tip in the thermoelastic images is shown in Fig. 5.

The precision of the technique can be clearly seen. The ease and accuracy with which

the crack tip can be located means that T S Ahas great potential in the study of crack

growth in complex structures with complex stress fields.

The ability to locate the crack tip automatically makes the measurement of the

fatigue crack growth rate much easier. Growth data for the repair weld is plotted

against the effective stress intensity factor range in Fig. 6.